Snøhetta's Trondheim office block is energy positive exemplar

‘Form follows environment’ is the mantra that guides Powerhouse Brattørkaia in Trondheim, the first office building in Norway that produces more energy than it uses. Designed by Snøhetta, it is energy positive in construction as well when all its figures cradle to grave are included. The building is expected to use 21kWK/m²/year, and has embodied energy amounting to 22kWK/m²/year, but will produce 49kWK/m²/year, enough to power neighbouring buildings and a fleet of the city’s electric buses through a local micro grid. Unusually, though, this is not the new headquarters for an on-the-pulse eco company, it is a speculative office for commercial tenants.

‘Buildings account for 40% of the world’s energy consumption,’ explains Rune Grasdal, Snøhetta senior architect and project manager for the scheme, by video call. ‘Energy positive construction is an important part of the solution to global warming.’

The project emerged out of an alliance of big companies in Norway, including Snøhetta, in 2010. The other parties are contractor Skanska, property company Entra, environmental organisation ZERO and consulting firm Asplan Viak. They met at a conference and decided the only way forward with sustainability was to set themselves as a group the challenge of producing zero emissions buildings.

 

A decade later, that goal no longer seems as ambitious as it would have then, yet the alliance has completed four projects, known as ‘powerhouses’ because they produce more energy than they use over their defined lifespan of 60 years, including construction, demolition and embodied energy. The energy they produce is renewable and clean. The first project was a 5,200m² refurbished 1980s office scheme just outside Oslo in Sandvika (‘the best thing is not to build at all’, says Grasdal). And next month  the group will complete Powerhouse Telemark, another office possibly even more striking than this one, but its second project was a school and it is also working on a hotel. 

At 17,800m², Brattørkaia is the largest to date. Like the others, it prioritises solar power to meet its energy needs. The requirement sets the building’s architect­ural expression as a kind of black iceberg that has inexplicably become neatly wedged into the fjord-side of downtown Trondheim, between otherwise ordinary looking buildings. From a distance, though, the slightly arched pointed top of its huge sloping roof forms another peak in the horizon of mountains behind. 

The aim of the project was threefold: to maximise the amount of clean energy produced by the building, to minimise the energy required to run it, and to serve as a pleasant space for its tenants and the general public. 

The building occupies a brownfield site next to a public plaza in the city’s former industrial port area, which has been redeveloping over the past 20 years. One neighbour is Entra’s headquarters, the other is a new business school commissioned by Entra. The site is an important route to the city centre for people arriving at/leaving from the speedboat terminal via an existing walkway and series of stairs and lifts over the railway tracks that needed to be integrated into the scheme.  

‘The main shape of the building was determined by planning regulations, building out to the maximum footprint by the public square,’ says Grasdal, ‘but the concept design was about finding the best way to collect sunlight.’

 

The principal design idea is the building’s vast south-facing sloping roof, which is covered in 2,006m² of solar cells that generate much of the building’s electricity. The roof is strategically angled to 19°, the closest possible to the optimum 30° that the planners would allow. Any steeper and the building would have been too much taller than its neighbours, but averaged out over the footprint, the 10 storeys was permissible. 

The elevations, meanwhile, all have a gentle bow outward, an architectural feature designed to express a ‘bursting with power’ analogy to the pentagonal plan. Like the roof, the south facade is entirely covered with solar cells (503m²), and part of the western one is too. Over a year, the cells are able to collect nearly 500,000kWh of green energy, with the near total daylight summer months compensating for the near total darkness of winter. A rack system on the roof allows for easier maintenance and prevents snow build-up collapses, although minimal snow is expected to settle in this location as it is so close to the sea and because the cells and building are black, absorbing what sunlight there is. 

All over, the solar cells graduate into the aluminium sandwich cladding panel facade, deliberately chosen in black to make them disappear and to discreetly infill the triangular gaps around the rectangular solar cells on the roof, creating an environmentally conscious building almost in disguise. 

‘We also wanted the building to look all like one. We didn’t want to express the solar panels,’ explains Grasdal.

In the middle of the roof, however, is a giant elliptical courtyard that appears completely circular when seen from the city centre because of the roof pitch. It also makes a spectacular frame for views out towards the city centre and the cathedral. In contrast to the all-black exterior, this area of the facade is clad in corrugated yellow panels, made of the same aluminium composite, that bring extra daylight into the deep office plan. The courtyard is publicly accessible via a tunnel through the building from the walkway level on the second floor. It is designed to form part of the ventilation system as well.

 

Yet solar is not the only means by which the building powers itself. It conceals multiple technologies that both radically reduce energy use for its daily operations and leverage surplus energy. The heating and cooling system includes a water-to-air heat exchange system connected to sea pumps – a system that operates in a similar way to ground source heat pumps by making the most of the building’s harbourside location in using the relatively stable 4°C temperature of deep water. Low-speed air circulates through the building from the basement via ventilation hubs in the lift and stair cores as well as through specially designed columns. The air is let out close to the floor, while the extraction takes place centrally by suppression in the stair shafts.

Meanwhile, triple glazed, sun protected, externally aluminium encased timber windows are extra large on the north elevation to make the most of the views to the fjord and maximise daylight, avoiding much need for artificial lighting. But the windows get progressively shorter and narrower as you go round the east and west elevations towards the south, to prevent too much solar gain. The building also employs a concept called ‘liquid light’, which allows the artificial light to smoothly dim or brighten according to internal activity, reducing energy demand. Together, these strategies mean Powerhouse Brattørkaia consumes only about half the amount of energy for lighting of a typical commercial office building of comparable size. 

Likewise, the plan itself is designed to maximise energy efficiency. All enclosed meeting rooms are positioned along the eastern elevation to ensure daylight heating can circulate in the largest spaces, preventing the small rooms from getting too hot. This combines with building’s structural system of low-emission concrete, which uses its thermal mass to absorb and retain heat and cold, to regulate the temperature in the building without using electricity. Automated windows help regulate night-time cooling alongside the stack-effect of the courtyard. 

 

Inside, this means that towards the facade, the underside of the structure is as exposed as possible to allow air circulation beneath. Acoustic panels therefore accumulate in the centre of the footprint where less cooling required. ‘There is always a conflict between heating/cooling and sound design,’ says Grasdal. What’s certain is that very few of the choices for the building were solely aesthetic ones – even the yellow panels on the external stair to the public walkway over the railway are primarily for wayfinding.

So, what does the building provide? 

On the ground floor by the main entrance there is a café that opens onto the plaza, a retail unit (currently a florist) and a visitor centre where people, particularly schoolchildren, can learn about the building and its sustainable attributes. There is also a 200-seat auditorium for use by the offices or for hire, as well as changing facilities and lockers to encourage users to arrive by bike. On the first floor is a canteen, daylit by rooflights surrounding the garden in the courtyard, and above there is office space for 600 desks, already let to tenants including construction and shipping companies.

 

For its efforts, Powerhouse Brattørkaia has received the BREEAM Outstanding certification, which doesn’t quite say enough about its impressive credentials. This project provides a wealth of inspiration for how to implement technologies that produce energy-positive, environmentally friendly buildings. But in Grasdal’s closing comments he fires a warning shot as well as expressing hope: ‘It’s important to understand you can’t build this building wherever you want. This is surrounded by public space, the challenge for many other sites are neighbouring buildings that cast shadows.

‘But Brattørkaia is also a building that expresses where we are in 2020. As new facade systems and more efficient solar panels develop, in future you may not need such an expressively sloped roof to achieve the same results. The cost of solar cells will also go down, it will take less energy to produce them and they will be available in different colours and textures.’ 

Back in Britain, if anything good is to come out of the government’s overhaul of planning right now, perhaps it’s that one of these modern mini power station should be integrated into each of the new regulated planning zones, making the space around them for each to thrive. Meanwhile for the Powerhouse Alliance, it is ramping up its goals in line with the Paris Agreement on embodied energy with the vision set for energy-positive and carbon neutral. 

---

RIBA + VITRA TALK: SNØHETTA Craig Dykers and Kjetil Trædal Thorsen, founding partners of the global office Snøhetta, will present some of the practice’s recent works and outline their trans-disciplinary approach to architecture and landscape.

Click here for more ideas on tackling the climate emergency

In numbers

430m Norwegian Krone
project cost (£36.9m)
17,800m²
GIA
2,867m²
area of solar panels 
458,457kWh
approximate total solar production per year